Means for controlling the candle power of luminous tubes



Jan. 5, 1954 A. ARVIDSSON ET AL ,665,

MEANS FOR CONTROLLING THE/C/IANDLE POWER OF LUMINOUS TUBES Filed June 20, 1950 2 Sheets-Sheet '1 X WW Hfforn 9 y.

Jan. 5, 1954 A. ARVIDSSON ET AL 4 MEANS FOR CONTROLLING THE CANDLE POWER OF LUMINOUS TUBES Filed June 20, 3.950

2 Sheets-Sheet 2 Patented Jan. 5, 1954 MEANS FOR CONTROL POWER OF LU den, assignors to Allmanna LING THE CANDLE MIN OUS TUBES Algot Arvidsson, Saltsjobaden, Hugo Elmlund, Vasteras, and Georg Sonesson, Enskede, Swe- Aktiebolaget, Vasteras,

poration Svenska Elektriska Sweden, a. Swedish cor- Application June 20, 1950, Serial No. 169,114 Claims priority, application Sweden June 20, 1949 9 Claims.

For controlling the candle-power of luminous tubes it is a general rule that the control device shall permit a sufficiently high voltage to be permanently available in order to prevent the tube from being extinguished. Furthermore, the device shall permit a current control within the required range. In the case of tubes with hot cathodes it is then usually necessary to have separate heating of the filaments and the possibility of controlling the heating current in relation to the tube current. When igniting the tube, the heating current, as well as the voltage between the electrodes, should be high, but before the tube current is raised by the control device it should be limited to a value close to zero. After that, when the tube current is increased, it is desirable that the heating current should be reduced automatically.

According to the principle of operation of the luminous tube, an impedance must be connected in series with the tube for the purpose of limiting the tube current to an appropriate value, and means are generally provided for igniting the tube, for instance an automatic starter connected in parallel with the tube. It has been found that for control purposes it is advantageous that this impedance should consist of a transductor, the special properties of which are particularly suitable, and which provides a means of readily varying the traversing alternating current. It has also been proposed to arrange transductors in special connections for controllin the heating current of the tubes in relation to the tube current.

The connections shown, however, all suffer from drawbacks. Thus, some of them are such that, even with only one tube, they require a plurality of transformers and transductors which together with the requisite auxilary apparatus constitute a rather bulky control equipment. In those cases where the device has been made with only one transductor, this has been connected to the primary of the transformer for the tube current, an arrangement which considerably complicates light control, and which does not allow a stable setting between highest intensity and extinguished tube.

Said drawbacks can be avoided by means of the present invention, which relates to a control device combining excellent control properties with a simple and space saving design, and furthermore allowing the parallel-connected igniter to be entirely dispensed with. The device refers to candle-power control of luminous tubes with hot cathodes, including one tube or two tubes 2 connected in series and arranged to be fed by a transformer which also provides voltage for the heating of the filaments of the luminous tubes. The distinguishing feature is that an adjustable impedance is included in the tube circuit on the secondary of the transformer.

The device according to the invention possesses several valuable properties. Thus, it represents a saving in separate transductors and transformers for the heating current, as the windings for the heating current are now arranged on the common transformer or by employing part of the tube current winding in auto connection. Another important feature is that the heating curburning voltage of the tube. When the tube ignites, a voltage transition takes place to the series-connected impedance, which prior to ignition had an insignificant voltage drop but which negative current-voltage dependence of the tube. Despite the increased tube current, the heating of the electrodes can be kept down to a reasonable value, as the heating voltage follows the tube voltage and diminishes with it.

The invention makes full use of the great advantages derived from employing only one trans- The fewer the elements of this kind, the

' to master the no-load current shunting the tubes with a resistor as described hereinafter, that portion of the no-load current which passes the tubes will be reduced to any desired low value.

The invention will be further described with reference to the accompanying four figures.

Figure 1 shows a control device with a common transformer for tube current and heating current, using a reactor, and the secondary of siahtl transformer being associated with a rheos a Figure 2 shows an arrangement using on the transformer secondary a device hereinafter referred to as a transductor and consisting of at least one ferro-magnetic core with windings b utilizing saturation phenomena on the core material, the transductor also being common to a number of tubes or groups of tubes.

Figured shows another embodimentof the invention using a transductor for each group of tubes.

Figure 4 shows a simplified form according to thelast mentioned type.

In Figure l, a connection 1 shown for two luminous tubes, 1 and 2, the filaments of which are connected to separate heating windingsof the transformer secondary 19. One end of the main secondary winding is connected to an intermediate tapping on the secondary winding for one of the filaments at the end of the series-connected tubes. The other end of said secondary winding is in series with a rheostat connected to an intermediate tapping on the secondary winding for the filament situated at the opposite end of the tubes. transformer is connected to an alternating-current source at t via a reactor 2| and a switch 5. Prior to ignition of the tubes, the entire resistance Zllmust be in circuit. Since the tube current is thenzero, the entire line voltage is applied across the transformer iii, and full heating power is obtained. The voltage-drop in the reactor will thenbe small, as only heating power is drawn. When the filaments are hot, the tubes will ignite, and this can take place at very low tube current. When the resistor 2a is reduced, the tube current will increase, and the voltage drop across the reactor increases, accompanied by a corresponding drop in the voltage across the transformer, which accommodates itself to the burning voltage of the tubes. The heating voltage will then also drop simultaneously with the tube voltage, and the redu'ced heating of the filaments will be compensated by the contribution to the heating provided bythe increased tube current. The resistance 21?, which is required for a relatively wide range of adjustments, must be designed for the purpose. It should be variable between about 100 ohms and about 390,000 ohms, and in order that the tube v,current shall follow the lightoutput curve,

it should have progressively changing resistance, or may consist of a plurality of fractional resistorswhich are progressively brought into circuit with a switch. The ratio of the transformer should be chosen so that the tube will be certain to ignite, and the reactor should be dimensioned to give the appropriate heating current characteristic as the reactor takes over the voltage from the transformer. The reactor may possiblybe dispensed with by designing the transformer as a leakage flux transformer. By varyingtli leakage flux of the transformer or by connecting a constant resistor in series with the tube the desired conditionsmay be fulfilled. In the case of small installations it is profitable to userheostats for the. control, but with larger numbers of luminous tubes the rheostat may be replaced bya transductor.

In Figures 2 and 3 two embodiments of the invent ion are shown for a larger number of luminous tubes; in the figures the number shown is four.. The tubes are suitably brought together into groups of two tubes, connected in series according to the arrangement described above. The tubesi, and 2 in each group are connected to the transformer l9 associated with said group.

According to Figure 2 the primary windings of the transformer [9 are series-connected and connected to the alternating current line at 5 via the On the primary side the reactor 22 and the switch 5. Within each group of tubes the primary winding of a transformer 23 is connected in series with the tubes. The secondary windings of all transformers 23 are connected in series with each other and with a transductor 24. The direct-current excitation of the latter is usually obtained from the line or from a current transformer or, as shown in the figure, from the voltage drop across a part of the reactor 22. In all cases it is suitable to arrange a rheostat 25, from. which voltage is supplied to the rectifier 26 and possibly via a time-lag device, consisting of resistors 2'! and a capacitor 28, to the excitation winding 29 of the transductor 24.

The mode of operation of the device is essentially the same as that according to the embodiment in Figure 2. It is possible to arrange a large number of groups of luminous tubes i, 2 with corresponding transformers IS, 23 and to control them with the common transductor 24. The intermediate transformers 23, by means of which the variable impedance is translated to the tube circuits, allow control to be effected in a low tension circuit which admits the use of a very small transductor. v

To permit the tubes to ignite at the lowest pos}; sible current, amounting to, about 0.1 milliampere, the no-load current of the transformers and the transductor may be largely reduced by connecting a resistor 30 in parallel with the tubes, which resistor will partly absorb said current.

In order to ensure smooth ignition, it is suit able to take the excitation voltage from part of the reactor, as shown in this figure. h I e The voltage drop across the reactor is at first very slight, and when the tube current is increased by adjusting the control the voltage drop will only increase gradually. The time-Jag device 27, 28 thus makes it possible when closing the switch 5 to obtain a smooth and continuous ignition up to the pre-set candle-power of the luminous tubes for any arbitrary settingof the rheostat 25. V V

In Figure 3, a corresponding arrangement is shown somewhat modified. The transformers !9, each of them being in serieswith a reactor 34, are thus connected in'parallel with the line 6, from which they may be disconnected with the switch 5. The intermediate transformers 23 are in this case replaced by transductors 3!,the excitation windings of which, in series withsuitably adaptedresistors 32 are connected in paral: lel and connected to the rectifier 26 which. is connected to the rheostat 25 and the current transformer 33. This embodiment entails a further reduction in no-load current which ,is de-. sirab'le to divert fromthe tubes, and its simple design allows additional parallel-connection of further groups of tubes,

In the arrangement of the invention according toFigures 2 and 3, ti1ereactors22 or 38 may of course be omitted ifthe transformers mare. de-, signed as leakage flux transformers. order to gain the desired time lag effect on the ex.- citation of the transductors, which is obtained when the voltage for this purpose is derived from the reactor, a small current transformer may be connected instead of said reactor.

Howevenit is desirable toreduce the dimenssions'fof the elements necessaryfor the control device, so that it can be incorporatedin the tube fittings and to occupy the smallest possible space.

Iii gure a-i aliansementis shown which fulfils these conditions and which provides very good control properties. This arrangement also enables a power factor as high as 0.8 to be obtained for the entire lighting installation at full current, without having to resort to phase compensating elements.

In Figure 4, i and 2 represent two series-connected luminous tubes. The filaments of the tubes are fed from separate secondary windings of a transformer 35. The tubes are shunted by a resistor The transformer is designed as a so-called leakage fiux transformer. Primary and secondary windings for the tube current are auto-connected and the latter winding is so apportioned on the transformer core that the desired degree of leakage is obtained. The luminous tubes and a transformer 36 are connected in series with the last mentioned secondary winding. The primary winding of the transformer is fed from an alternating-current line at 6. 5

denotes a double-pole switch in that circuit. The

transducer i schematically shown with the two cores 3?, 33, the alternating-current windings 39, 56 having uni-directional valves 4! connected in series lor the purpose of self-excitation, and the direct-current fed windings 42, 43 and 4 3, G5. The windings d2, 43 are connected in series and connected to a rectifier bridge 26, supplied from the alternating-current line via a current transformer 33 and a rheostat 25. The windings 4d, d5 are also series-connected and connected to a rectifier bridge 45 energized by the heating voltage of th tubes. Said voltage may suitably be derived from the heating voltage winding of transformer e5, supplying two parallel-connected filaments. The excitation polarity of windings 42, t3 coincides with that of the excitation provided by the uni-directional valves 4!, whereas windings 44, 45 have opposite polarity.

When the luminous tubes are lit at the lowest possible initial candle-power, followed by a control action to increase the light output by means of the rheostat 25, the latter should be so adjusted, that when closing switch 5 the lowest possible voltage is applied to the rectifier 2t.

When closing the switch 5, power is at first drawn from the line mainly for the purpose of heating the tube filaments. The voltage across the latter will then be as high as possible owing to the fact that the transductor 36 so far has not taken up any voltage, and therefore the whole line voltage is applied to the tubes. The high voltage across the filaments will then also be used to keep the transductor excitation at a low level as the windings 44, 45, which oppose the other excitation windings, will be traversed by their maximum current before the tubes have ignited. After a short while, about half a second, the tubes will ignite, which occurs instantaneously, at a very low current. Immediately after ignition, when current begins to traverse the tubes, a leakage flux will develop in the transformer 35, however, which results in a diminution of the secondary voltage. This is favourable both from the point of view that the tube voltage has a tendency to drop with increasing tube current, and because the heating voltage should decrease as the tube current begins to contribute to the heating or" the filaments. The transformer 35 is suitably designed so that the heating voltage at full candle-power is about of the heating voltage prior to ignition. By increasing the excitation of the transductor by means of the rheostat 25 the current traversing the tubes Will increase and with it the candle-power. The leakage flux of the transformer increases and thus causes a progressive diminution of the secondary volt age. The effect of this is to lower the current traversing the opposing excitation winding 44. 45 resulting in a further increase in the tube current.

It is also possible when lighting the tubes, to have the rheostat adjusted to a fixed value, cor responding to the desired final candle-power. and in this manner obtain a gradual and smooth lighting action. If in thi case the switch 5 is closed, the maximum heating voltage will be ap plied to the filaments in exactly the same way as described above. As only a very slight current is required for the purpose, the current transformer 33 will supply a very low voltage to the rheostat 25 and the transductor excitation will be maintained at a low value by the small current through the windings 42, 43 and by the current through the windings M, 45, which current will be rather high owing to the heating voltage. After ignition of the tubes, when current has begun to traverse the tubes, the current from the current transformer 33 is increased at the same time as the current through the windings 44, 45 will be decreased. The transductor 36 will then be able to transmit a progressively increasing alternating-current, and the candle-power of the tubes will rise to the final value, determined by the setting of rheostat 25.

By designing the leakage flux transformer 35 with an auto-connected winding for the tube current, which winding should be divided on the two legs of the core, a distinct leakage flux will be obtained. The leg supporting the primary winding carries a suflicient number of secondary turns to ensure that the tubes obtain sufficient voltage to burn at full candle-power, while on the other leg are wound so many secondary turns that the tubes will ignite without fail.

The dimensions of the transductor 35 can be small and its sensitivity large owing to the selfexcitation provided by the valves II.

By connecting further groups of tubes provided with the requisite transformers and transductors to the conductors 47 and 48 it is possible to achieve simultaneous control of all the tubes by means of the common rheostat 25.

We claim as our invention:

1. A device for controlling the light output from luminous tubes equipped with hot cathodes, comprising in combination two series-connected luminous tubes, means for heating the filaments of said tubes, means for supplying discharge current to the tubes, an adjustable impedance element, means for adjusting the impedance of said element, said means for heating the filaments and said means for supplying discharge current being constituted by secondary windings on a transformer common to both purposes, and an alternating current source, the primary of said transformer being connected to said alternating current source, and said adjustable impedance element being inserted in the tube circuit on the secondary of said transformer.

2. A device according to claim 1 in which said adjustable impedance consists of an adjustable resistor, a reactor being connected in circuit with the primary of said transformer.

3. A device according to claim 1 in which said adjustable impedance consists of a transductor, means for supplying excitation current to the latter, means for adjusting said current, said current being derived from said alternating current source by rectifying means connected in the 

